1. Field of the Invention
The present invention relates to an accelerator device which is used in for example an electronic control throttle system of an engine for vehicle. More specifically, the present invention relates to an accelerator device adapted to apply hesteresis to the pedal effort between depression force and return force on an accelerator pedal in order to improve the feel of the accelerator pedal in operation.
2. Description of Related Art
Conventionally, there has been known an electronic control throttle system using no accelerator cable as one of systems or apparatuses mounted on an engine for vehicle and others. The electronic control throttle system of this type includes an accelerator device constructed to detect a depressed amount of an accelerator pedal as an accelerator opening degree by an accelerator sensor. A throttle opening degree of the electronic control throttle system is controlled based on the accelerator opening degree detected by the accelerator sensor.
With respect to the above type, there have already been proposed many accelerator devices adapted to produce hysteresis between depression force and return force on an accelerator pedal in order to improve the operational feel of the accelerator pedal. Under these circumstances, the applicant of the present invention proposed an accelerator device in Japanese patent unexamined publication No. 2002-79844. This accelerator device includes easy-to-mount parts used for providing hysteresis to the pedal effort (pedal force) on the accelerator pedal and can produce the pedal effort hysteresis by stable movements.
As shown in FIG. 14, this accelerator device is provided with an accelerator arm 61 including an accelerator pedal on a tip part thereof, a support case 63 internally holding a base part 61a of the accelerator arm 61 (an arm base part) while rotatably supporting the arm base part 61a through a support shaft 62, a return spring 64 urging the accelerator arm 61 to rotate in a returning direction, thereby returning the accelerator pedal to an initial position, and an accelerator sensor 65 for detecting the rotation amount of the accelerator arm 61 as an accelerator opening degree. In addition, a friction member 66 having a tip end surface 66a which is held in contact with an inner surface 63a of the support case 63 is attached to the arm base part 61a. This friction member 66 is rotatably supported to the arm base part 61a through a support pin 67. The return spring 64, constructed of a tension spring, is tensioned between a part of the friction member 66 close to its tip and a spring hook 63b of the support case 63 in order to press the tip end surface 66a of the friction member 66 against the inner surface 63a of the support case 63. With the above structure, the rotation of the accelerator arm 61 causes the tip end surface 66a of the friction member 66 to slide along the inner surface 63a of the support case 63. Thus, as shown in FIG. 15, predetermined hysteresis is produced between depression force and return force on the accelerator pedal.
In the accelerator device described in the above publication, however, a stick slip (a catch) would occur in some cases while the tip end surface 66a of the friction member 66 is caused to slide along the inner surface 63a of the support case 63, thus impairing a smooth feel of the accelerator pedal.
It is surmised that this stick slip is caused when the strain occurring during the sliding of the tip end surface 66a of the friction member 66 along the inner surface 63a of the support case 63 returns in an instant. FIG. 16 shows the friction member 66 modeled into a “cantilever beam”. In this figure, the tip of the cantilever beam corresponds to a “friction part”. The spring force F and the pedal effort P act in mutually perpendicular directions at the tip end of the cantilever beam. The strain δ in this tip end is expressed by the following modeling formula (1). It is conceivable that the stick slip of the friction member 66 can be reduced when the device is adapted to minimize the strain δ:δ=β·P·I3/E·M  (1)wherein “β” is a predetermined coefficient, “I” is the length of the “beam”, “E” is a longitudinal elastic coefficient, and “M” is the geometrical moment of inertia of the “beam”, respectively.